Gut Bugs Tied to Preemie Infections

Uniformity in the bacterial composition of low birthweight infants' gut, mouth, and skin after birth may leave them open to potentially fatal infections, researchers found.

Across a six-infant sample of low birthweight infants, patients' bacterial microbiomes were ripe, at times, with bacteria associated with neonatal infections and necrotizing enterocolitis, according to Elizabeth Costello, PhD, a postdoctoral scholar at Stanford University School of Medicine, and colleagues.

Analysis of these infants showed "a delayed compositional differentiation of the oral cavity and distal gut microbiota, and, in the case of one infant, an abundant, uncultivated oral Mycoplasma sp., recently detected in human vaginal samples," they wrote online in the journal mBio.

The authors explained that a number of postnatal outcomes -- such as receipt of antibiotics, enteral feedings, and prolonged hospital stays -- "can influence or be influenced by interactions with microbes."

Additionally, diversifying a disrupted gut flora environment -- such as through fecal transplant -- has been associated with resolution of recurrent Clostridium difficile infections.

"Postnatal microbial colonization prompts the terminal maturation of host intestinal structures, mediates the development of the immune system, and induces resistance to invasion by would-be pathogens," the authors noted.

They tracked the distal gut, oral cavity, and skin surface microbiota of six hospitalized low birthweight infants -- including two sets of twins -- over the second and third weeks of their lives to look at microbiota composition and compare the sample's microbial environment with that of age-matched normal birthweight infants in the distal gut and in a sample of adults in all sites.

They cautioned that "although the infants sampled were unaffected by sepsis or necrotizing enterocolitis, their age range represents an important window of vulnerability for both of these conditions."

The study sample included five infants who were born premature -- at less than 32 weeks of gestation -- and half were considered "very low birthweight" at less than 1.5 kg, where they were "at highest risk for complications of preterm birth."

Among low birthweight infants, Staphylococcus and Streptococcus were abundant in all body sites, as opposed to just on the skin and saliva where they are "characteristically found," they noted. Additionally, the "body site-driven composition differentiation in the low birthweight infants seemed lower than that reported for healthy adults."

Composition between infants was "relatively stable over time," where "subtle yet important temporal changes" occurred at around days eight to 21, where oral and fecal bacteria began to differentiate substantially "largely driven by progressive temporal turnover in the distal gut." The rate of differentiation was very similar to that seen in normal birthweight infants.

A body site comparison between the two groups showed the effect of body site was smaller in the low birthweight infants versus healthy adults.

The authors found that among body sites, infants' skin was most similar to adult skin microbiota composition, possibly due to the high exposure to adult skin or because the infants' skin was more selective for adult skin bacteria.

Stool and saliva presence of Staphylococcus decreased modestly as the patients grew older (P=0.011 for stool, P=0.064 for saliva), but age was not otherwise associated with differences in bacterial community composition. Stool and saliva bacterial composition did not differ significantly between patients until 15 days.

They noted that the window where there was a lack of differentiation may be one in which potentially fatal infections would be most likely to creep in, as noted by the presence of oral and gut Staphylococcus and Streptococcus.

The authors cautioned that the data were collected from a small patient sample and that their research was subject to a number of uncontrolled variables, such as gestational age at delivery, multiple gestation, medical treatment, and delivery mode. Their data were not generalizable, but they added that further studies of a larger, well-controlled, prospective cohort would be a worthwhile follow-up.

The study was supported by the NIH, the Walter V. and Idun Berry postdoctoral fellowship, the March of Dimes Foundation, and the Thomas C. and Joan M. Merigan Endowment.

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